The effect of structural modifications of the flavin cofactor on the redox properties of flavodoxins will be determined so as to elucidate the pathway of electron transfer in these proteins. The reactivity of the fully reduced proteins will also be studied to investigate the effect of protein binding on flavin redox chemistry. Chemical modification of the active site methionine residue in Clostridium flavodoxin will be carried out to ascertain the role of this amino acid side chain in determining redox properties. Isolation and characterization of the flavoprotein photoreceptor for Euglena phototaxis will be attempted.